Productivity of seedlings of Scots pine on alluvial sands of natural and man-made origin

Abstract

Purpose. To find out quantitative physical and water indicators for which there are significant changes in forest vegetation properties in alluvial sands, as well as to trace their impact on the formation of pine seedling root systems and the accumulation of aboveground phytomass in their plantations. Methodology. The chemical properties of sandy soils were determined taking into account the current requirements of ISO, and their physical and water properties using volumetric cylinders, followed by the calculation of their density, porosity, as well as the coefficients of water content and aeration. The root population of the upper meter layer of sands was determined by the method of monoliths, and plant productivity was assessed by phytomass of medium model trees (7-year-old seedlings, plots 14) and by biometric indicators (22-year-old seedlings, plots 59). Findings. It was found that on alluvial sands with a density of 1.501.66 g × cm-3 in their upper meter thickness, 7-year-old seedlings of Scots pine form a superficial root system (1341.8 g × m-2), which provides accumulation of 2558 kg × ha-1 of aboveground phytomass in seedlings. As the density of sands increases, the production of seedling phytomass decreases. In the case of an increase in density by 14% (1.521.72 g × cm-3), there is a decrease in the mass of roots, in a meter-thick layer of sand (by 53.4%) and aboveground phytomass (by 36%). An increase in the density of sands by 510% with its maximum values (1.741.79 g × cm-3) in a 1030 cm layer causes a decrease in the mass of pine roots by 64.1%. The roots of pine seedlings, for such a density of sand, are not able to inhabit the inter-row space, as indicated by their content in the upper 20-cm layer of sand (2% of the mass of small roots recorded in a one-meter thickness). The phytomass of aboveground organs decreased by 81%, and the seedlings themselves were marked by dwarf growth (were grown by V class of productivity). On sands covered with humus mass of zonal soils, the one meter thickness contained fewer (by 51.4%) pine roots (482.8 g × m-2) than on the control. The share of small roots was smaller (by 61.5%) and that of coarse roots was higher (by 21.5%). Losses of aboveground phytomass per unit area in pine seedlings growing under such conditions can reach 31%, due to the compaction of sands at a depth of 2550 cm (1.671.72 g × cm-3) when they are covered by humus mass and row spacing are overgrown with herbaceous plants (root mass in 60-cm profile 3147 g × m-2) in the phase of their individual growth. Originality. Quantitative indicators of density, porosity and coefficients of water content and aeration of alluvial sands of natural and man-made origin are shown for which the seedlings of Scots pine feature delay in the formation of full-fledged root systems of the surface type, which is reflected in a decrease in the productivity of pine plantations cultivated on the sands, up to the visual manifestation of their dwarf growth. Practical value. The quantitative indicators of their physical and water properties obtained for alluvial sands explain the changes occurring in the structure of the root systems of Scots pine seedlings and the productivity of their aboveground organs. Maintaining the density of sands in the range of 1.501.66 g × cm-3 will allow growing pine seedlings on sands without covering their surface with humus mass, and no-till pre-planting loosening of sands in the rows of future crops allows ensuring the cultivation of multifunctional pine plantations.